The present invention pertains to electrodes, and in particular to adjustable segmented electrodes used in plasma processing of workpieces such as semiconductor wafers.
In semiconductor manufacturing, plasma reactor chambers are used to remove or deposit material on a workpiece (e.g., semiconductor substrate) in the process of making integrated circuit (IC) devices. A key factor in obtaining the highest yield and overall quality of ICs is the uniformity of the etching and deposition processes.
A problem that has plagued prior art plasma reactors is the control of the plasma to obtain uniform workpiece etching and deposition. In plasma reactors, the degree of etch or deposition uniformity is determined by the uniformity of the plasma properties. The latter is dictated by the design of the overall system, and in particular the design of the electrodes used to create the plasma in the interior of the reactor chamber.
One approach to improving etch and deposition uniformity has been to use a segmented electrode. FIG. 1 is a plan view of one type of prior art segmented electrode 800. Electrode 800 is circular in shape and comprises a central electrode segment 806, and four arcuate-shaped outer electrode segments 810 surrounding the central electrode segment. Electrode segments 806 and 810 are made of a conducting material, such as aluminum or aluminum covered with silicon on the front surface facing the plasma. Each electrode segment 806 or 810 is electrically connected to a RF power supply (not shown) that provides power to the electrode segment. Though nominally identical, the RF signal being applied to one electrode segment is likely to differ from that being applied to adjacent electrode segments in power (voltage or current or both at the same time), frequency, phase, or even waveform. Even the phase difference in RF between adjacent sub-electrodes (i.e., electrode segments) can be sufficient to cause electrical discharging between electrode segments when the dielectric separation between them is small.
Accordingly an insulating structure 816 supports and separates respective electrode segments 806 and 810 to prevent electrical communication (e.g., discharging) between the segments when RF power is supplied to the segments. Insulating structure 816 is typically non-adjustable and made of a ceramic material or glass.
Unfortunately, even with a segmented electrode such as electrode 800 of FIG. 1, etch and deposition non-uniformities can occur when processing a workpiece. In particular, when plasma etching a substrate with a segmented electrode, it is expected that regions underneath the insulating structure 816 have a different etch or deposition rate than regions directly underneath the sub-electrodes. The overall non-uniformity is typically-up to 10% for a 200 mm capacitively coupled plasma chamber with an unsegmented plasma electrode. A successful implementation of a segmented electrode for a capacitive plasma chamber is expected to achieve non-uniformity less than about 5% when a partition shown in FIG. 1 is used, due to the smaller dimensions of the sub-electrodes. However, there are a number of issues that need to be addressed when a partitioned plasma electrode is used for a capacitively coupled plasma chamber, such as a discharge between adjacent sub-electrodes and RF interference among sub-electrodes.
There are several U.S. patents pertaining to segmented electrodes used in plasma processing. These include U.S. Pat. Nos. 4,885,074, 5,565,074 and 5,733,511. The segmented electrodes disclosed in these patents are not adjustable in position.